1. Field of the Invention
The present invention relates to an optical pickup actuator and an optical disc drive using the same.
2. Description of the Related Art
Optical disc drives generally include an optical pickup used to record or reproduce information on, or from, a disc that is rotated by a spindle motor. Such an optical pickup records information on the disc by radiating light onto the disc via an objective lens, or reproduces information from the disc by receiving light reflected from the disc. The optical pickup includes an actuator for controlling the position of the objective lens so that light is radiated onto a correct position of the disc.
FIG. 1 illustrates a conventional optical pickup actuator. Referring to FIG. 1, the optical pickup actuator includes a blade 2 on which an objective lens 1 is mounted, and a plurality of wires 6, which support the blade 2 so that the blade 2 moves relative to a holder 3. A focusing coil 4 and tracking coils 5 are installed in the blade 2 to form electrical paths for driving the objective lens 1 in a focusing direction F and a tracking direction T. A pair of magnets 7 and a pair of yokes 8 interact with current flowing through the focusing coil 4 and the tracking coils 5 to generate an electromagnetic force to drive the blade 2 in the focusing direction F and the tracking direction T.
However, in the above-described structure, the effective length of the focusing coil 4 that may be used for driving the blade 2 is less, e.g., only about ¼ of the total length thereof. In other words, as shown in FIG. 2, only an effective portion 4a of the focusing coil 4, i.e., front portion between the pair of magnets 7 is used for driving the blade 2. Leakage flux of the pair of magnets 7 affects other portions of the focusing coil 4, i.e., rear, left, and right portions 4b, 4c, and 4d respectively. However, since current flows through the left and right portions, 4c and 4d respectively, in opposite directions, forces acting in the left and right portions, 4c and 4d respectively, are offset. Though a force acting in the rear portion 4b is weaker than a force acting in the front portion 4a, the direction of the force generated in the rear portion 4b is opposite to the direction of the force generated in the effective front portion 4a. This opposition may result in a decrease in the sensitivity for controlling the blade 2 and may cause an auxiliary resonance in the actuator.
In other words, as illustrated in FIG. 2, a resultant force affecting the blade 20 is substantially at most a value of F1−F2+F3−F4 for driving forces generated at front, rear, left, and right portions, F1, F2, F3 and F4, respectively.
In order to solve these problems, a method of adhering spacers to attempt to block a magnetic force from flowing onto the rear surfaces of the yokes 8 to block the leakage flux into the rear, left, and right portions 4b, 4c, and 4d, respectively, except to the effective portion 4a, has been proposed. However, in this method, the number of parts and the number of processes of assembling the optical pickup actuator increase. Therefore, an optical pickup actuator having a structure to improve the efficiency of focusing and tracking such coils is necessary.